Nearly all classes of active wearable and implantable biomedical devices rely on some form of battery power for operation. Heart rate monitors, pacemakers, implantable cardioverter-defibrillators and neural stimulators together represent a broad subset of bio-electronic devices that provide continuous diagnostics and therapy in this mode. Although advances in battery technology have led to substantial reductions in overall sizes and increases in storage capacities, operational lifetimes remain limited, rarely exceeding a few days for wearable devices and a few years for implants (Karami & Inman, “Powering pacemakers from heartbeat vibrations using linear and nonlinear energy harvesters”, Appl. Phys. Lett., 100:042901 (2012); Kerzenmacher, et al., “Energy harvesting by implantable abiotically catalyzed glucose fuel cells”, J. Power Sources, 182:1-17 (2008); Mateu & Moll, “Review of energy harvesting techniques and applications for microelectronics”, Proc SPIE, 5837:359-373 (2005)). Surgical procedures to replace the depleted batteries of implantable devices are thus essential, exposing patients to health risks, heightened morbidity and even potential mortality (Mallela, et al., “Trends in cardiac pacemaker batteries”, Indian Pacing Electrophysiol. 1, 4:201-212 (2004)). The health burden and costs are substantial.
Investigations into energy harvesting strategies to replace batteries demonstrate several unusual ways to extract power from chemical, mechanical, electrical and thermal processes in the human body (Starner, “Human-powered wearable computing”, IBM Systems J, 35 (3&4):618-629 (1996)). Examples include use of glucose oxidation (Kerzenmacher 2008; Halamkova, et al., “Implanted biofuel cell operating in living snail”, J. Am. Chem. Soc., 134:5040-5043 (2012)), temperature gradients (Cuadras, et al., “Thermal energy harvesting through pyroelectricity”, Sens Actuators A Phys., 158:132-139 (2010)), chemical energy via biogalvanic cells (Reynolds L W, “Utilization of bioelectricity as power supply for implanted electronic devices”, Aerosp. Med., 35:115-117 (1964)), electric potentials of the inner ear (Mercier, et al., “Energy extraction from the biologic battery in the inner ear”, Nat. Biotechnology, 30: 1240-1243 (2012)), mechanical movements of limbs and natural vibrations of internal organs (Wischke, et al., “Piezoelectrically tunable electromagnetic vibration harvester”, J. Micromech. Microeng., 20(3):035025 (2010); Wong L S, et al., “A very low-power CMOS mixed-signal IC for implantable pacemaker applications”, IEEE J Solid-State Circuits, 39:2446-2456 (2004)). Such phenomena provide promising opportunities for power supply to wearable and implantable devices that interface with the body. A recent example involves a hybrid kinetic device integrated with the heart for applications with pacemakers (Zurbuchen A, et al., “Energy harvesting from the beating heart by a mass imbalance oscillation generator”, Annals of Biomed. Eng., 41(1):131-141 (2013)). More speculative approaches, based on analytical models of harvesting from pressure-driven deformations of an artery by magneto-hydrodynamics, also exist (Pfenniger, et al., “Energy harvesting through arterial wall deformation: design considerations for a magneto-hydrodynamic generator”, Med. Biol. Eng. Comput., 51(7):741-755 (2013)).
Cardiac and lung motions, in particular, serve as inexhaustible sources of energy during the lifespan of a patient. Mechanical to electrical transduction mechanisms in piezoelectric materials may offer viable routes to energy harvesting in such cases. Proposals exist for devices that convert heartbeat vibrations into electrical energy using resonantly coupled motions of thick (1-2 mm) piezoelectric ceramic beams on brass substrates (Karami (2012); Karami & Inman, “Equivalent damping and frequency change for linear and nonlinear hybrid vibrational energy harvesting systems”, J. Sound Vib., 330:5583-5597 (2011)).
While such models highlight the potential for self-powering devices, there are important practical challenges in the coupling of rigid mechanical systems with the soft, dynamic surfaces of the body in a manner that does not induce adverse side effects. Piezoelectric materials are rigid materials that could restrict movement of the tissue to which they are attached. Flexible devices based on arrays of piezoelectric ZnO nanowires (NWs) are being developed (Wang, et al., “Direct current nanogenerator driven by ultrasonic wave”, Science, 316:102-105 (2007); Song & Wang, “Piezoelectric nanogenerator based on zinc oxide nanowire arrays”, Science, 213:242-246 (2006); Xu, et al., “Integrated multilayer nanogenerator fabricated using paired nanotip-to-nanowire brushes”, Nano Lett., 8:4027-4032 (2008)).
Experiments performed with a linear motor to periodically deform the device indicate electrical outputs as large as 1-2 V (open-circuit voltage) and 100 nA (short-circuit current) (Zhu, et al., “Flexible high-output nanogenerator based on lateral ZnO nanowire array”, Nano Lett., 10:3151-3155 (2010)). Initial in vivo tests on rabbit hearts yielded voltages and currents of ˜1 mV and ˜1 pA, respectively. However, the associated electrical power is substantially less than that required for operation of existing classes of implants, such as pacemakers. Some improvement in performance is possible with thin film geometries, as demonstrated in bending experiments on devices based on BaTiO3 (Park, et al., “Piezoelectric BaTiO3 thin film nanogenerator on plastic substrates”, Nano Lett 10:4939 (2010)) and PZT (Chen, et al., “1.6 V Nanogenerator for mechanical energy harvesting using PZT nanofibers”, Nano Lett., 10: 2133-2137 (2010); Qi, et al., “Enhanced piezoelectricity and stretchability in energy harvesting devices fabricated from buckled PZT ribbons”, Nano Lett., 11:1331-1336 (2011)).
However, there is a need to develop materials and devices that generate greater amounts of power.
Therefore, it is an object of the invention to provide improved materials, devices, and/or systems for generating, and optionally storing and/or telemetering electrical power sufficient to power medical or other devices without requiring replacement of the battery.
It is a further object of the invention to provide improved methods for powering devices, particularly medical devices.